Vinylidene olefin, which are branched monoolefins having the structure (R.sup.1)(R.sup.2)C.dbd.CH.sub.2 where R.sup.1 and R.sup.2 are the same or, more usually, different alkyl groups, are of commercial importance as raw materials for use in producing-double tailed oxo alcohols and other functionalized derivatives, used in the manufacture of detergents, surfactants, specialty agricultural chemicals, and fuel or lubricant additives. Vinylidene olefins can be produced by dimerizing vinyl olefins.
U.S. Pat. No. 4,155,946 to Sato, Noguchi and Yasui discloses a process for dimerizing lower .alpha.-olefins in which the catalyst system is formed from (1) a trialkylaluminum compound, (2) a salt or complex of nickel, (3) a trivalent phosphorus compound selected from specified groups, and (4) a halogenated phenol.
U.S. Pat. No. 4,709,112 to Sato, Ikimi, Tojima and Takahashi describes a process for dimerizing lower .alpha.-olefins which uses a catalyst system formed from (1) a trialkylaluminum compound, (2) an organic salt or complex of nickel, (3) a trivalent phosphorus compound selected from specified groups, (4) a fluorinated isopropanol, and (5) a catalyst co-activator selected from specified types of halogenated compounds.
U.S. Pat. No. 4,973,788 to Lin, Nelson and Lanier describes a process for dimerizing a vinyl olefin monomer at a selectivity of at least 85 mol percent. This is accomplished by use of a catalyst which consists essentially of 0.001-0.04 mols of trialkylaluminum per mol of vinyl olefin, and conducting the reaction at a temperature in the range of about 100.degree.-140.degree. C. for a time sufficient to convert at least 80 mol percent of the initial vinyl olefin to a different product. The reaction rate under these conditions is quite slow, and thus a long reaction time is required. For example it is pointed out that the time required for 90 percent conversion at 120.degree. C. with 0.043 mols of aluminum alkyl catalyst per mol of initial vinyl olefin is about 94 hours, and that with 0.017 mols of the catalyst per mol of initial vinyl olefin the time required at 120.degree. C. is about 192 hours. It is also shown in the patent that although the reaction is faster at 172.degree. C. compared to 120.degree. C., the selectivity to vinylidene dimer is only 71 weight percent compared to 90 weight percent with the same catalyst concentration but at 120.degree. C.
The vinylidene dimerization reaction with a trialkylaluminum catalyst involves the catalytic interaction (perhaps transitory coupling) between the vinyl olefin and the aluminum alkyl. As indicated in U.S. Pat. No. 4,973,788, supra, the dimerization is effected at temperatures of 100.degree.-140.degree. C. It has now been found that at these and higher temperatures, isomerization of vinyl olefin to internal olefin can occur. This competitive reaction reduces dimerization product yield, because these isomers do not further react to produce the desired vinylidene olefin product.
During olefin displacement reactions, isomerization of linear 1-olefins is known to occur when trace amounts of certain metals, especially nickel, react with the aluminum alkyl catalysts. For example, Ziegler et at., Justus Liebigs Ann. Chem. Volume 629 at pages 25 and 62 (1960) mentioned using phenyl acetylene to reduce isomerization in olefin displacement reactions catalyzed by nickel. To the same general effect is U.S. Pat. No. 5,124,465 to Allen, Anderson, Diefenbach, Lin, Nemec, Overstreet and Robinson. In The Use of Aluminum Alkyls in Organic Synthesis, Ethyl Corporation, page 53 (1977), it is stated "The isomerization of the .alpha.-olefin by the nickel catalyst can be suppressed by addition of small amounts of acetylene hydrocarbons, but by and large this modification of the displacement has not been developed to perfection."
It would be extremely desirable to be able to achieve high selectivity to vinylidene dimer in a dimerization process without requiring use of the extremely long reaction periods deemed necessary in accordance with the process of U.S. Pat. No. 4,973,788 and without need for multicomponent catalyst systems such as described in U.S. Pat. Nos. 4,155,946 and 4,709,112, especially if the dimerization reaction can be conducted using nickel-containing reaction vessels, transfer lines, and like reactor auxiliaries, and without concern about possible presence of trace amounts of nickel-containing impurities in the feeds to, or on the walls of, the reactor.
The present invention has accomplished this goal, and made it possible to achieve all of these highly beneficial results.